An anchoring bolt of that kind is described in DE-OS No. 29 41 769. The conical undercutting is produced in the case of the known anchoring bolt by the cooperation of rod profiling and the presence of abrasive grains in the mortar capsule. The anchoring bolt executes a staggering motion in which the insertion end, with its profiling, is moved in a more or less defined path. The abrasive grains of the mortar capsule, in the case of the known anchoring bolt, are pulled along intermittently with a component of motion in the circumferential direction during the drilling-in movement and, as a result of their being alongside the insertion portion, they are forced along the walls of the cylindrical pre-bore. The exact shape of the undercutting results as a matter of chance and it is not excluded that a cross-section through the undercutting is oval instead of round.
If the known anchoring bolt should be used for anchoring in a so-called parting zone, a defined undercutting is desirable. In particular it is advantageous of the undercut has circular symmetry, since it cannot be foreseen in which direction the cracks that may possibly appear will run.